David's Astronomy - Notes 2022-03-25 (S995)

Issue.
Unexpectedly slow dome rotation during slew to UGC 4219 (20:35)

Description.
Slew from 185.0 to 199.7° (14.7°) recorded as taking 238s, a rotation speed of only 0.06°/s instead of a normal speed of 0.5 to 2.2°/s.

The SlewTable shows a D*' suffix on the row associated with slew to UGC 4219, which was a feature added 2022-02-26 (CI, S976) to highlight abnormally slow dome slews. Because of the 'slow' rotation the log file contains a dump out of the domepath which is useful for analysis (DumpSlewPointsToLogFile() routine added this feature 2022-02-26 (CI, S976) with a bug fix 2022-02-27 (SD, S977)).

Analysis (Dome Slew).
The 'domepath' listing shows that the Dome Slew took 7.5s to move from 185.0 to 197.7° (speed 1.7°/s), but then rested at 197.7° before moving to 198.7° after 123.6-124.5s, and then moving from 198.7 to 199.7° between 235.9 and 237.4s.

The 'domepath' listing shows that the Dome Slewing flag switches from 1 to 0 after 7.5s, which should have marked the end of the dome slew at that point, but somehow didn't.    The later movements (marked by the slewing flag temporarily switching back to 1) are possibily related to scope tracking as the movements correspond to 1° changes in required dome azimuth.     The slew monitoring loop in the SlewTheSkyScope() routine is designed to time out after 4 minutes (240s) and this seemed to have happened on this occasion.

There is no evidence to indicate that the problem is related to any physical / mechanical issue with the dome slew, but is more likely related to a bug in the slew monitoring.

Examination of AstroMain code and dome path data would imply tthat bDomeSlewStarted was set to True after 0.5s, that bDomeSlewStopped was set to True after 7.5s (with LastSlewSeconds set to 7.5s), and that bDomeCompleted was set to True after 8.2s. This fully indicates that DomeSlew was completed after 7.5s. But why does the slew table report a 238s dome slew ?.

The reason would seem to be the subsequent minor dome movements related to telescope tracking ? or continued slow telescope slewing, caused the bDomeSlewStopped flag to be reset to False which led to a revised LastSlewSeconds of 237.5s when the Dome stopped slewing again at 237.5s. This has only been picked up because Scope slewing was seemingly still ongoing after 240s.

Scope Slew (Scope Slew):
Scope Slew from Az/Alt 186.4°/53.9° to 199.9° / 70.7° (an angle of 21.6°) was recorded as taking 240s (or a speed of 0.09°/s, which is exceedingly slow) before the slew monitoring loop timed out after 4 minutes (240s), and aborted the slew.

The log file shows that scope had reached Az/Alt 199.91°/70.93° after 9.9s and had become effectively stabilised at Az/Alt 199.80° / 70.74° after 16.8s, but then made intermittent 0.5 deg movements between 16.8s and 240s The Scope.Slewing flag instead of turning back to 0 (false) after 9.8-16.8s continued showing Slewing 1 (True). The SlewTheSkyScope() routine continued with bScopeCompleted = false until the moment that slew monitoring timed-out after 4 minutes (240s).

It is hypothesized there was some glitch that caused this particular telescope slew to not complete the final part of the slew. Plate Solution of the 1st locate frame showed that calculated telescope pointing error was abnormally large (being a value of 42.76' vs a normal pointing error after other slews of only 0.5' to 2.8'). Issue closed after review 2022-05-10, and is put down as rare unexplained glitch.

Conclusion
So it is actually the scope slewing which was unexpectedly slow ! (raised as a separate issue). AstroMain 3.51.5 modified so that bDomeSlewStopped can only be reset within the first 20s of a slew, and LastSlewSeconds can't be set to 240s (if a later dome movement has to be aborted when bDomeCompleted has already been set to True, but an issue with scope slew completion delays the end of dome rotation monitoring).

Closed after review and small code improvements 2022-05-10 (AstroMain 3.51.5)


	Session Aims & Highlights
	- Observing Result - Night Summary Plot - Session Event Log

	Operational Issues
	- Critical Issues (0), Major Issues (0), Minor Issues (3), Small Defects (1), Continuous Improvement (3)

	Images from 2022-03-25 >> [ Local Files >> ]

	Investigation - Slow Dome Slew / Slow Scope Slew to one particular target (UGC 4219, 20:35)

This Web Page:	Notes - Session 995 (2022-03-25)
Last Updated :	2024-03-22
Site Owner :	David Richards
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David's Astronomy Pages
Notes - Session 995 (2022-03-25)

Session Aims & Highlights (2022-03-25)

Operational Issues (2022-03-25, S995)

Investigation - Slow Dome Slew / Slow Scope Slew to one particular target (UGC 4219, 20:35)

David's Astronomy Pages Notes - Session 995 (2022-03-25)

Session Aims & Highlights (2022-03-25)

Operational Issues (2022-03-25, S995)

Investigation - Slow Dome Slew / Slow Scope Slew to one particular target (UGC 4219, 20:35)

David's Astronomy Pages
Notes - Session 995 (2022-03-25)